Detergent agglomeration often involves the use of a highly viscous semi-solid (paste) binder. Such binders do not penetrate or disperse into a powder bed in the absence of an external force. Therefore mechanical dispersion is often employed to facilitate binder dispersion. Understanding the binder dispersion process is vital in ensuring consistent product quality. The present study aims to describe how viscous surfactant binders will undergo fragmentation/breakage within the mixer. The semi-solid binder can be considered to be “particles” and these powder coated binder particles (PCBPs) undergo a size reduction process with time. Other factors that influence the rate at which this size reduction process will occur include impeller speed, particle size and morphology. A typical detergent formulation will consist of a mixture of surfactant, zeolite (powder) and soda ash (powder). Two different grades of soda ash powder were studied: 130 μm light ash particles and 11 μm ground ash particles. This study reveals that larger particles maybe capable of exerting larger forces leading to more rapid breakage and deformation of the coated semi-solid binder fragments. This study also reveals that rougher particles are capable of penetrating the surface of the binder to a greater extent than smoother ones. In the case of zeolite, due to its smaller, more spherical particles and compact structure, the intermolecular forces within the semi-solid binder may be able to oppose the applied force (impact from the particles at the boundary) to a greater extent. This explains the slow change in the mean diameter of the zeolite PCBPs with time compared with the other two powders. At higher shear rates, there does not appear to be a significant increase in the final mass of the PCBPs when compared to the trials done at lower shear, instead the time taken to reach steady state in terms of both size and mass is shortened for all three powders, and for light and ground ash the lifespan of the PCBPs are shortened significantly, as the system passes the nucleation step and enters the wet-agglomerate regime. To conclude larger and rougher particles, with better flowability will disperse the highly viscous binder more effectively in a moving bed of powder. A high shear rate is recommended for better initial dispersion of the binder into powder formulations that consist of a large proportion of fine material.
Balashanmugam, M., Cheong, Y. S., Alam, Z., Hounslow, M. J., & Salman, A. D. (2016). Dispersion of a semi-solid binder in a moving powder bed during detergent agglomeration. Chemical Engineering Research and Design, 110, 32–42. https://doi.org/10.1016/j.cherd.2016.03.029